Process for removing impurities in the recycling of lithium-ion batteries

ABSTRACT

A method of treating a leaching solution derived from a black mass from spent lithium-ion batteries comprising setting pH of the leaching solution to about pH 1.2 to 2.5, adding iron powder to induce copper cementation, adding lime after copper cementation, and after adding lime, transiting pH of the leaching solution to about pH 6 to extract calcium fluoride, titanium hydroxide, aluminium hydroxide, iron hydroxide, and iron phosphate. A black mass recycling system comprising an impurity removal reactor configured to receive a sodium hydroxide feed, an iron powder feed, and a lime feed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of International PatentApplication No. PCT/SG2021/050496, which has an international filingdate of 24 Aug. 2021 and claims priority to and benefit under 35 U.S.C.§ 119 to U.S. Provisional Application No. 63/069,488 filed on 24 Aug.2020. The contents of each application recited above are incorporatedherein by reference in their entirety.

FIELD OF INVENTION

The present invention generally relates to a method for recycling spentlithium-ion batteries. More particularly, it relates to a method forremoval of impurities from a leaching solution of spent lithium-ionbatteries.

BACKGROUND

Lithium-ion batteries contain valuable precious metals which would go towaste when the batteries are spent and discarded. With the rising use oflithium-ion batteries, the recovery of precious metals from spentlithium-ion batteries have become an important industry.

Typically, spent lithium-ion batteries are dismantled, crushed, orshredded to form a black mass to prepare them for recycling. Currentlithium-ion battery recycling efforts are often primarily focused onrecovering the precious metals cobalt and lithium from lithium cobaltoxide cathodes. However, there are many other types of cathode materialsused in lithium-ion batteries. A significant portion of these cathodematerials include other precious metals such as nickel and manganese.Conventional recycling methods do not adequately handle the recycling ofdifferent types of lithium-ion battery cathode materials and fail tosufficiently address the extraction of these other precious metals.

Further, black mass, especially those derived collectively fromdifferent types of lithium-ion batteries contains many types ofimpurities. Failing to effectively remove them adversely affects thepurity of precious metals recovered from recycling. Present efforts ofimpurity removal involve numerous steps requiring many reactors andfilters. Not only does this lengthen the entire recycling process, butwith each reactor or filter, valuable material is lost along the wayresulting in a severe reduction in the amount of precious metalsavailable for recovery.

Thus, there exists a need for a lithium-ion battery recycling processwhich can better handle the removal of impurities in black mass,especially that derived collective from different types of lithium-ionbatteries. There also exists an associated need to remove impurities ina more efficient way that requires less equipment and results in lessreduction in the amount of precious metals available for recovery.

The invention seeks to answer these needs. Further, other desirablefeatures and characteristics will become apparent from the rest of thedescription read in conjunction with the accompanying drawings.

SUMMARY

In accordance with the present invention, a method of treating aleaching solution derived from a black mass is provided. The methodcomprises setting pH of the leaching solution to about pH 1.2 to 2.15,adding iron powder to induce copper cementation, adding lime aftercopper cementation, and after adding lime, transiting pH of the leachingsolution to about pH 6 to extract calcium fluoride, titanium hydroxide,aluminium hydroxide, iron hydroxide, and iron phosphate. Preferably,about 2.5 g of iron powder is added for each litre of the leachingsolution. More preferably, the iron powder may be added over a period ofabout 15 minutes. Preferably, the lime is calcium oxide and about 20-40g of calcium oxide is added for each kg of black mass. Alternatively,the lime is calcium hydroxide and about 30-60 g of calcium hydroxide isadded for each kg of black mass. Preferably, the leaching solution isderived from the black mass by leaching the black mass with sulfuricacid and hydrogen peroxide. Preferably, the sulfuric acid is 4M sulfuricacid, and about 6 litres of sulfuric acid is added for each kg of theblack mass. Preferably, about 50 ml of hydrogen peroxide (30%concentration) per litre of solution is added. Preferably, the sulfuricacid and hydrogen peroxide are added in consecutive order. The methodmay further comprise agitating the black mass, sulfuric acid, andhydrogen peroxide for a period of 1 hour. The method may furthercomprise diluting the sulfuric acid to 2M by adding deionised waterafter the period of 1 hour.

In another aspect, a black mass recycling system is provided. The blackmass recycling system comprises an impurity removal reactor configuredto receive a sodium hydroxide feed, an iron powder feed, and a limefeed. Preferably, the black mass recycling system may further comprise aleaching reactor configured to receive a sulfuric acid feed, a hydrogenperoxide feed, and a deionised water feed, and a first valved outletassociated with the leaching reactor providing fluid communicationbetween the leaching reactor and the impurity removal reactor. Morepreferably, the black mass recycling system may further comprise animpurity removal agitator provided within the impurity removal reactor,and a leaching reactor agitator provided within the leaching reactor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a process flow diagram of a process of leaching and removal ofimpurities.

FIG. 2 is a graph (Graph 1) showing the effect of pH on coppercementation over time.

FIG. 3 is a graph (Graph 2) showing the effect of pH on fluorideconcentration in solution.

FIG. 4 is a graph (Graph 3) showing the effect of pH on the iron,aluminium and titanium concentration.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof. The processes andsystems described in the detailed description and drawings are forillustrative purposes and are not meant to be limiting. Otherembodiments can be utilised, and other changes can be made, withoutdeparting from the scope of the disclosure presented herein. In thepresent disclosure, the depiction of a given element or consideration oruse of a particular element number in a particular Fig. or a referencethereto in corresponding descriptive material can encompass the same, anequivalent, or an analogous element or element number identified inanother Fig. or descriptive material associated therewith.

Black mass is poured from its holding container 100 into a firstreactor, namely a leaching reactor, 102. The black mass may collectivelyinclude lithium-ion batteries with cathodes made from lithium cobaltoxide (LCO), lithium manganese oxide (LMO), lithium nickel manganesecobalt oxide (NMC), lithium iron phosphate (LFP), lithium nickel cobaltaluminium oxide (NCA), and lithium titanate (LTO). As a result, theblack mass comprises impurities of iron, copper, fluorine, phosphorous,titanium and aluminium.

In the first phase of leaching, an inorganic acid, preferably sulfuricacid (H₂SO₄), provided from an inorganic acid source 110 is added to theblack mass in the first reactor 102, forming a solution. Preferably, aproportion of about 1 kg of black mass to about 6 litres of 4M sulfuricacid is observed. The inorganic acid may optionally be hydrochloric acidsubject to adjustments to quantities of the reagents described belowwhich should be apparent to a skilled person.

Hydrogen peroxide (H₂O₂), preferably about 50 ml of hydrogen peroxide(30% concentration) per litre of the solution, is provided to thecontents of the first reactor 102 from a hydrogen peroxide source 112 tofacilitate leaching as a co-digestant. The contents of the first reactor102 undergoes agitation by an agitator 132, preferably for about 1 hour.During the first phase of leaching, the sulfuric acid increases theavailability of sulfate ions (SO₄ ²⁻) which react with iron present inthe black mass to form ferrous iron (Fe²⁺). The hydrogen peroxide thenoxidises the ferrous iron (Fe²⁺) to ferric iron (Fe³⁺). The ferric ironthen reacts with the sulfate ions to produce iron sulfate (Fe₂(SO₄)₃).

In the second phase, deionised water is added into the first reactor 102from a deionised water source 114 to dilute the sulfuric acid in thefirst reactor 102, preferably to about 2M. Agitation of the contents ofthe first reactor 102 is maintained by the agitator 132 for about 30minutes.

During both the first and second phases of leaching, the temperature ofthe contents in the first reactor 102 should be maintained at 70-90° C.A skilled person should readily understand that the amount of sulfuricacid, hydrogen peroxide and deionised water may be adjusted according tothe amount of black mass processed.

After the first and second phases of leaching, the leaching solutionfrom the first reactor 102 is released via an outlet valve 136 andtransferred into a second reactor 104 by way of a pump 142. Thefollowing describes the processes of removing the impurities copper,fluorine, phosphate, iron, titanium, and aluminium from the leachingsolution in the second reactor 104, during which the contents of thesecond reactor 104 are continually agitated by an agitator 134.

Sodium hydroxide (NaOH) from a sodium hydroxide source 116 is added tothe leaching solution in the second reactor 104 to set the pH of theleaching solution at a value of about pH 1.2 to 2.15. Iron (Fe) powderis added from an iron powder source 118, preferably about 2.5 g of ironpowder per litre of leaching solution, to the leaching solution overabout 15 minutes while maintaining the temperature of the contents ofthe second reactor at about 60° C. Capitalising on the reductivecapacity of ignoble metals on noble metal ions according to theelectromotive force series (i.e., voltage gap between two half-cellreactions corresponds to higher propensity of reaction from athermodynamic and electrochemistry standpoint), the iron powder willreact favourably with copper in the leaching solution, leading to thecementation of copper:Fe+Cu²⁺→Fe²⁺+Cu

FIG. 2 records the effect of copper cementation over a period of 60minutes as a result of setting the pH of the leaching solution at 1.2,2.15 and 3.07 respectively. The concentration of copper in the leachingsolution is taken and computed to give a copper removal percentageduring the period of 60 minutes as follows:

$\frac{{In{itial}{concentration}{of}{copper}} - {{final}{concentration}{of}{copper}}}{{Initial}{concentration}{of}{copper}} \times 100$

It is observed that setting a pH of 1.2 or 2.15 results in thecementation of about 90% of copper in the leaching solution, that is,copper removal. When the pH is set at 3.07, cementation of copper in theleaching solution drops to below 80% over the same period.

The sulfuric acid and hydrogen peroxide added from the first phase ofleaching in the first reactor 102 forms part of the contents of thesecond reactor 104. The hydrogen peroxide oxidises the ferrous iron(Fe²⁺) formed during copper cementation to ferric iron (Fe³⁺). Theferric iron reacts with the sulfate ions to produce iron sulfate(Fe₂(SO₄)₃).

Some fluoride may be removed during the leaching process in the firstreactor 102, but sufficiently undesirable and toxic amounts which mayresult in capacity attenuation of lithium-ion batteries that mayeventually be produced will remain as fluoride ions in the leachingsolution transferred to the second reactor 104. Lime is added from alime source 120 to the contents of the second reactor 104, preferablyabout 20-40 g of calcium oxide or about 30-60 g of calcium hydroxide perkg of the black mass previously added into the first reactor 102. Afterthe addition of lime, the contents of the second reactor 104 is left torest (with continued agitation) for a period of about 30 minutes atabout 40° C.

Lime should be added only after the iron powder has completed thecementation of copper from the contents of the second reactor 104 toavoid the lime interfering with the capacity of the iron powder toinduce copper cementation.

After the rest period of about 30 minutes, more sodium hydroxide isadded to the second reactor 104 to transition the pH of its contents toabout pH 6. The pH transition triggers precipitation of the otherimpurities (fluorine, iron, phosphorus, titanium, and aluminium) in theleaching solution transferred from the first reactor 102 to the secondreactor 104. From about pH 2.2, fluoride starts to precipitate ascalcium fluoride (CaF₂):CaO+2HF→CaF₂(s)+H₂O

FIG. 3 records the concentration of fluoride in the leaching solutionthat started at an initial concentration of 650 mg/l after 60 minutes atpH 2.27, 3.12, 4.06 and 5.24 respectively. It is observed that theconcentration of fluoride is reduced consecutively and significantly atpH 3.12, 4.06 and 5.24, while the concentration of fluoride is not assignificantly reduced at pH 2.27.

As the pH of the contents of the second reactor 104 rises to about pH 3,the sodium hydroxide causes iron ions, whether originally in theleaching solution or added for copper cementation, to precipitate asiron hydroxide. The remaining iron that is not precipitated as ironhydroxide reacts with phosphate ions (PO₄ ³⁻) in the contents of thesecond reactor 104 to precipitate as iron phosphate (FePO₄).

TABLE 1 The effect of pH on iron (Fe) and Phosphorus (P) precipitationpH Fe(%) precipitation P(%) Precipitation 2.5 — — 3 10.74 13.51 3.559.45 51.68 4 100 89.12 4.5 100 100

Table 1 records the percentage of iron and phosphorus originallyexisting in the leaching solution which were precipitated as ironphosphate at pH values between pH 2.5 to 4.5 over 60 minutes. It isobserved that precipitation occurred from pH 3 and increases at each pHvalue observed through to pH 4.5 where essentially all iron andphosphorus which existed in the leaching solution were precipitated.

As the pH of the contents of the second reactor 104 rises to and exceedspH 4, the hydrogen peroxide which was added in the first reactor 102 andtransferred in the leaching solution to the second reactor 104 pushesthe oxidative states of titanium and aluminium to titanium (V) andaluminium (III) respectively, thus initiating precipitation of theirhydroxides Ti(OH)₄ and Al(OH)₃.

Once the pH reaches about pH 6, the contents of the second reactor 104is left to rest (with continued agitation) for about 60 minutes at about60° C. After the period of 60 minutes, the contents of the secondreactor 104 is released from the second reactor 104 by an outlet valve138 and is passed through a filter 148 to remove copper and theprecipitates (calcium fluoride, iron phosphate, iron hydroxide, titaniumhydroxide, and aluminium hydroxide), thereby removing a significantamount of the impurities that originally existed in the black mass.

FIG. 4 records the concentration of aluminium, iron and titanium in theleaching solution that started at an initial concentration of 2.26, 0.2,and 1.1 g/l respectively after of a period of 30 minutes at pH 3.21,4.16, 5.08 and 6.12 respectively. The concentration of aluminium, ironand titanium in the leaching solution is taken and computed to give aremoval percentage after the period of 30 minutes as follows:

$\left( \frac{{In{itial}{concentration}} - {{final}{concentration}}}{{Initial}{concentration}} \right) \times 100$

It is observed that the concentration of aluminium, iron and titaniumreduced significantly at pH 4.16, 5.08 and 6.12 compared to pH 3.21.

The leaching process in the first reactor 102 and precipitationreactions in the second reactor 104 take about 3-4 hours in total, atthe end of which less than 10 mg/l of impurities from the black massremains in the contents of the second reactor 104.

While various aspects and embodiments have been disclosed herein, itwill be appreciated by a person skilled in the art that several of theabove-disclosed structures, parameters, or processes thereof, can bedesirably modified, adapted and combined into alternative structures,processes and/or applications. It is intended that all suchmodifications, alterations, adaptations, and/or improvements made to thevarious embodiments that are disclosed come within the scope of thepresent disclosure. The various aspects and embodiments disclosed hereinare for purposes of illustration and are not intended to be limiting,with the true scope of the disclosure being indicated by the followingclaims.

The invention claimed is:
 1. A method of treating a leaching solutioncomprising: setting pH of the leaching solution to about pH 1.2 to 2.15,wherein the leaching solution is derived from a black mass comprisingiron, copper, fluorine, phosphorous, titanium, and aluminium; addingiron powder to induce copper cementation; after copper cementation,adding lime; and after adding lime, transiting pH of the leachingsolution to about pH 6 to extract calcium fluoride, titanium hydroxide,aluminium hydroxide, iron hydroxide, and iron phosphate.
 2. The methodaccording to claim 1, wherein about 2.5 g of iron powder is added foreach litre of the leaching solution.
 3. The method according to claim 1,wherein the iron powder is added over a period of about 15 minutes. 4.The method according to claim 1, wherein the lime is calcium oxide andabout 20-40 g of calcium oxide is added for each kg of black mass. 5.The method according to claim 1, wherein the lime is calcium hydroxideand about 30-60 g of calcium hydroxide is added for each kg of blackmass.
 6. The method according to claim 1, wherein the leaching solutionis derived from the black mass by leaching the black mass with sulfuricacid and hydrogen peroxide.
 7. The method according to claim 6, whereinthe sulfuric acid is 4M sulfuric acid and about 6 litres of sulfuricacid is added for each kg of the black mass.
 8. The method according toclaim 6, wherein the sulfuric acid and hydrogen peroxide are added inconsecutive order.
 9. The method according to claim 6, wherein the blackmass, sulfuric acid and hydrogen peroxide are agitated for a period of 1hour.
 10. The method according to claim 9, further comprising dilutingthe sulfuric acid to about 2M by adding deionised water after the periodof 1 hour.
 11. A black mass recycling system comprising: an impurityremoval reactor configured to receive a sodium hydroxide feed, an ironpowder feed, and a lime feed; a leaching reactor configured to receive asulfuric acid feed, a hydrogen peroxide feed, a deionised water feed,and a black mass feed comprising iron, copper, fluorine, phosphorous,titanium, and aluminium; and a first valved outlet associated with theleaching reactor providing fluid communication between the leachingreactor and the impurity removal reactor.
 12. The black mass recyclingsystem of claim 11, further comprising an impurity removal agitatorprovided within the impurity removal reactor; and a leaching reactoragitator provided within the leaching reactor.